Accurate detection and/or quantification of components in liquids is used in a plurality of applications. The accuracy of detection and/or quantification is not only dependent on the quality of the sensor by which the component is sensed, but typically also requires compensating for background and/or environmental effects that are present during the detection process. Such background and/or environmental effects may include a variety of effects such as for example drifts in sensing elements, temperature effects, other environmental effects, the presence and/or absence of other components in the liquid to be characterized, slow shifts in the composition of the liquid to be characterized.
A plurality of techniques for generating a reference signal is known. The most commonly known technique is the recording of a reference signal using a blank measurement. When performing a blank measurement, typically a measurement is performed with a reference sample or without a sample being present. This reference signal is then used for compensating the measured sensor used for characterizing. A disadvantage of using a blank measurement is that it typically is pre-recorded, thus not guaranteeing the same conditions as those present during the measurement. Using a blank measurement does typically not allow to bring into account effects on or by components of the liquid which do not need to be characterized, but certainly are necessary to take into account for accurate correction.
Another well-known principle to enhance the signal-to-noise of a set-up is to work ‘dual-beam’. This means that a signal arm is created that is in contact with the substance that you want to sense and an identical reference arm is created that feels the same environment except for the substance that should be detected. By taking the ratio of the signal and reference measurements, the influence of the substance is revealed. This can be explained by the fact that all the common variations, caused by fluctuations in e.g. temperature, pressure, absorption etc. cancel out. Nevertheless, it is not easy to provide a proper reference sample.
One particular example is shown in U.S. Pat. No. 6,049,727, where an implantable sensor is presented. The sensor is developed for in vivo measurement of the spectra of body fluids. Light is emitted at a plurality of wavelengths and the absorption is determined after the light passes through the fluid. To compensate for drift of the laser diodes a portion of the output of the laser diodes is diverted to a calibration detector. This calibration allows to compensate for drift of the laser diodes, it however does not allow to compensate for changes in the medium through which the light is passing or any other environmental conditions influencing the system behavior.
Therefore there is still room for improvement in systems and methods for liquid characterisation.